1. Field of the Invention
The present invention relates to a stamper for use in forming a large number of convex lens comprising resin having a high refractive index upon a surface of glass substrate, and also to a method for producing a plate-like micro-lens array by use of the stamper.
2. Description of Related Art
A flat-type or plate-like (planar) micro-lens array is installed into, for example, a part of a liquid crystal display element. Explaining a structure of such a liquid crystal display element by referring to FIG. 7, a gap is formed between glass substrates 101 and 102 by a spacer 103, into which liquid crystal 104 is poured. On a surface of the glass substrate 101 there are formed opposing electrodes 101a at the side of the liquid crystal 104, and on a surface of the other glass substrate 102 there are formed transparent pixel electrodes 102a at the side of the liquid crystal 104. Further, additional portions other than the transparent pixel electrodes 102a are formed which are not transparent, such as wiring, TFTs (thin film transistors), etc.
Next, upon an exterior surface of the glass substrate 101 there is bonded a planar micro-lens array 105, serving to focus irradiated light through the lens portion 106 thereof into pixel electrodes (i.e., openings for the pixels) 102a, so as to increase the brightness of an image projected upon the screen. Not that the pixels and lenses (lens elements) are provided in plural numbers.
An example of the method for producing such a planar micro-lens array 105 will be explained by referring to FIG. 8 attached.
First, recessed portions 111 are formed on the surface of the glass substrate 110 through an etching process, and then a resin of high refractive index 112 is applied thereupon and is spread over the surface of the glass substrate 110 by a stamper 113 so as to fill in plural recessed portions 111. Next, the high refractive index resin 112 is cured under light, thereby obtaining the lens portion 106 mentioned above.
However, in the case of producing or forming the planar micro-lens array with the method mentioned above, any of the high refractive index resin that is excess is pushed or forced out from the edge of the glass substrate and is cured during the curing process. As a result, the planar micro-lens array itself becomes larger in dimension thereof, such that it cannot be bonded or attached on the other element(s) and its size does not fit with the other portions for installation therewith. This is a disadvantage. Further, if the high refractive index resin exudes to the reverse of the substrate, the planar micro-lens array will experience degraded performance.
Furthermore, when a plurality of planar micro-lens arrays are cut out from a large-sized glass substrate on which multiple surfaces are formed, since the high refractive index resin forms a layer applied over the entire surface of the glass substrate, the layer of the high refractive index resin might be easily separated or exfoliated therefrom, or the surface of the micro-lens array may be damaged during a subsequent cutting procedure.
Therefore, the applicant of the present application already proposed a structure, disclosed in Japanese Patent Application No. Hei-7244288 (1995), in which a gutter portion 113 is formed surrounding the outside of the recessed portions 111 so as to receive or accommodate any high refractive index resin that exudes in excess therefrom, as shown in FIG. 9.
However, a problem lying in the method shown in Japanese Patent Application No. Hei-7244288 (1995) is that since the etching is performed on the glass substrate itself forming the planar micro-lens array, the etching must be performed on the glass substrate every time before applying the high refractive index resin thereon.
Further, as shown in FIG. 9, the gutter portion 113 is formed at the same time that the recessed portions 111 are formed by the etching, and therefore the depth of it comes to be same to those of the recessed portions 111. As a result, there is a possibility that the gutter portion 113 will have insufficient volume, though it may still be partially adequate. Nonetheless, any excess high refractive index resin cannot be accommodated or received therein with certainty.